Toothbrush with elastomer filled flexible head

ABSTRACT

The invention relates to a toothbrush comprising:  
     i) an elongated handle having distal and proximal ends and one or more elastomeric handle regions therein; and  
     ii) a resiliently flexible head attached to the proximal end of the handle, the head including a pair of opposing faces, one of the pair being a bristle-bearing face with bristles attached to and extending from the face, wherein at least one of the pair has one or more elastomer-containing, transverse grooves therein; and  
     iii) one or more elastomer supply channels extending between the elastomeric handle regions and the transverse grooves,  
     whereby at least one of the elastomeric handle regions and the transverse grooves can be filled with elastomer from a single injection point.  
     The elastomeric regions in the head can be used to make the head flexible and the whole brush can conveniently be made on conventional machines.

CROSS REFERENCE TO CO-PENDING APPLICATION

[0001] This application is a continuation of U.S. application Ser. No.09/101,918 filed Aug. 20, 1998, which was the National Stage ofInternational Application No. PCT/US97/00968, filed Jan. 17, 1997, thesubstances of which are incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The present invention relates to a toothbrush, more particularlyto a toothbrush with a comprising regions of elastomer in both the headand the handle wherein one or more elastomer supply channels connect theregions so that they can all be filled with elastomer from a singleinjection point.

BACKGROUND OF THE INVENTION

[0003] The configuration of human teeth requires that the ideal bristlecontour for toothbrushes for brushing the buccal or outside surfaces ofteeth be concave and that the ideal bristle contour for brushing thelingual or inside surfaces of teeth be convex. Most brushes have asingle piece head which is of comparable thickness to the handle andwhich is relatively rigid and of a fixed curvature or configuration.

[0004] A further drawback of conventional brushes is that pressing thebrush sufficiently hard against the teeth to get good cleaning risksdamaging or discomforting the softer, adjacent gums. To a certain extentthis can be solved by modifying the configuration of the brush, or byvarying bristle hardness or length, though again, a single configurationcannot be optimum for all circumstances.

[0005] Some brushes may, however, incorporate a means for allowing thehead to flex relative to the handle, as described for example inEP-A-371,293. Even so, such brushes have limited effectiveness. Otherbrushes are known which are adjustable into several different but fixedconfigurations. Adjustable toothbrushes are often difficult tomanipulate and may be unreliable.

[0006] WO 92/17093 discloses a toothbrush having a handle and at one endthereof a bristle-bearing head, wherein the head is in the form of twoor more segments flexibly and resiliently linked to each other and/or tothe handle, one or more of the segments being bristle bearing. In oneembodiment this is achieved by the use of transverse, and optionallylongitudinal, grooves on the opposite face of the head to the bristles.The grooves can be wholly or partially filled with an elastomer.

[0007] Co-filed application WO 92/17092 further discloses a toothbrushhaving a handle and at one end thereof a bristle-bearing head which isflexibly and resiliently linked to an extended portion of the handle.The space between the head and the handle may be filled with anelastomer. The applicant markets a brush called the ‘Schwingkopf’ underthe name ‘Dr. Best’ which contains some of the features disclosed in WO92/17092. The brush has an elastomeric handle grip and an elastomerfilled groove connecting the grip to an elastomer filled region in theneck of the brush. However, the brush does not contain transversegrooves in the head.

[0008] It is well-known to provide elastomeric grips in the handles oftoothbrushes. It is also known from the above-mentioned PCT applicationsto provide transverse grooves containing elastomer into a brush head. Tothe present applicant's knowledge however, it has not been disclosed howboth these objects can be achieved using a conventional single-point,injection moulding process.

[0009] It has now been found that all of the elastomer filled areas ofthe brush can be filled by a single-point injection moulding process byproviding one or more elastome supply channels which connect the groovesin the head to the grips in the handle.

[0010] It is accordingly an object of this invention to provide atoothbrush with a flexible head and handle grips which can be made by asimple injection moulding process.

[0011] It is yet a further object of this invention to provide atoothbrush which has good long-term durability.

SUMMARY OF THE INVENTION

[0012] According to one aspect of the present invention there isprovided a toothbrush, comprising:

[0013] i) an elongated handle having distal and proximal ends and one ormore elastomeric handle regions therein; and

[0014] ii) a resiliently flexible head attached to the proximal end ofthe handle, the head including a pair of opposing faces, one of the pairbeing a bristle-bearing face with bristles attached to and extendingfrom the face, wherein at least one of the pair has one or moreelastomer-containing, transverse grooves therein; and

[0015] iii) one or more elastomer supply channels extending between theelastomeric handle regions and the transverse grooves,

[0016] whereby at least one of the elastomeric handle regions and thetransverse grooves can be filled with elastomer from a single injectionpoint.

[0017] According to a second aspect of the invention there is provided atoothbrush, comprising:

[0018] i) an elongated handle having distal and proximal ends and one ormore elastomeric handle regions therein; and

[0019] ii) a resiliently flexible head attached to the proximal end ofthe handle, the head including a pair of opposing faces, one of the pairbeing a bristle-bearing face with bristles attached to and extendingfrom the face, wherein each of the pair has one or moreelastomer-containing, transverse grooves therein, the grooves dividingthe head into segments which are flexibly connected by hinges, whereineach hinge is located between the opposing faces and at a distance of atleast about 10% of the depth of the head from each of the faces, thehinges being less than the full width of the head; and

[0020] iii) one or more elastomer supply channels extending between theelastomeric handle regions and the transverse grooves,

[0021] whereby at least one of the elastomeric handle regions and thetransverse grooves can be filled with elastomer from a single injectionpoint.

[0022] The toothbrush of this invention comprises a handle includingelastomeric regions, which can be used to improve the user's grip on thehandle, and a head which has transverse grooves that allow the head toflex under the action of brushing and accommodate itself to, forexample, the differing profiles of individual users' teeth. The headfurther includes elastomer contained within the grooves on at least oneface. The elastomer improves the resilience of the head by acting like aspring, so that when a force applied to bend the head is removed, thehead returns within a short period of time to its originalconfiguration. The toothbrush further comprises one or more supplychannels which connect the elastomeric regions in the handle to thetransverse grooves in the head enabling the elastomer in both the headgrooves and handle regions to be supplied from a single elastomerinjection point. The grooves divide the head into segments and definehinges which connect the segments. Preferably, there are transversegrooves on both of the opposing faces and the hinges are located betweenthe faces so that they are subject to the minimum amount of tension orcompression. In this case the hinges are preferably less than the fullwidth of the head so that elastomer can flow from one face of the had tothe opposing face. The interconnectivity of the elastomer containingparts enables all of them to be filled with elastomer using asingle-point injection moulding process on conventional equipment.

DETAILED DESCRIPTION OF THE INVENTION

[0023] Handle

[0024] The toothbrush of this invention comprises an elongated handlehaving distal and proximal ends and one or more elastomeric handleregions therein. The handle can be of shape and external dimensionsuitable for toothbrushes. The elastomeric regions in the handle aregenerally designed to act as hand or finger grips but they can beprovided for solely aesthetic purposes, for example to give the brush adistinctive appearance. The elastomeric regions can be flush with thesurface of the handle or raised or recessed from the handle surface.Preferably at least a part of one elastomeric region is raised forproviding better grip. In general the elastomeric regions are providedby initially moulding the handle the handle to comprise voids which arethen filled by the elastomer in a separate injection moulding step. Thevoids provide some physical entrapment of the elastomer, but preferablythe elastomer is chosen so that it becomes bonded to the handle materialthrough the injection moulding process. The voids can be arranged sothat when filled with elastomer the various elastomer regions, at leastwhen handle material is opaque, give the appearance of being completelydiscrete. At least one, preferably all, of the elastomeric regions inthe handle is connected by the elastomer supply channel(s) describedbelow to the transverse grooves in the head. Typically, the elastomer inthe grips of the handle is a substantial part of the total volume ofelastomer to be injected. For this reason the elastomer injection pointis preferably located at the distal end of the handle. In this context,‘at the distal end of the handle’ means that the injection point islocated closer to the distal end than to the proximal end of the handle.

[0025] The handle, and also the toothbrush head, are generally made ofrelatively non-compressible materials, preferably with a modulus ofelasticity of at least about 500 MPa, more preferably at least about1000 MPa, which are conventional in the manufacture of toothbrushes,especially plastics materials. Suitable plastics materials include, forexample, polyamides and polypropylenes. Polypropylene is preferred.Suitable polypropylenes include the material ‘Polypropylene PM 1600’(marketed by Shell), having a modulus of elasticity (ISO 178) of 1500MPa and Apryl 3400 MA1 from Elf Atochem. Preferably, a foaming agentsuch as Hydrocerol HP20DP from Boehringer-Mannheim is mixed with thepolypropylene at a level of from about 1% to about 3%, preferably fromabout 1.5% to about 2.5%, by weight of the polypropylene. The foamingagent assists the flow of the polypropylene during moulding and, inparticular, helps to ensure uniform formation of the hinges in the head.

[0026] Suitable elastomers for use herein include thermoplasticelastomers with a Shore hardness of 30-80 and a modulus of elasticity ofless than about 500 MPa, preferably less than about 300 MPa, such asSantoprene and Thermoflex. An exemplary elastomer is ‘PTS Thermoflex 75’(marketed by Plastic Technologie Service, Germany), having a modulus ofelasticity (ISO 178) of 100 MPa and a hardness (ISO 868) of 80 Shore A.Elastomers PL12291, PL12292, and PL12293 (marketed by Multibase, SaintLaurent Du Pont, France) are also suitable for use herein. In general,choosing the elastomer so that is based upon the same chemical class ofpolymers as material of the head segments assists in bonding theelastomer to the head segments. For example, when the head segments aremade from polypropylene, the elastomer is preferably based uponpolypropylene. The elastomers can optionally be mixed with a suitableplasticiser or foaming agent to make them more compressible. The colourof the elastomer material can be the same as that of the head segments,or it may be different thereby achieving a distinctive striped orotherwise patterned appearance.

[0027] The handle itself is generally rigid. Optionally, the handle maycomprise a neck portion which is more flexible than the rest of thehandle, as known in the art, provided that it is sufficiently rigidthat, in use, when force is applied to the head, particularly whenbrushing the teeth, the head still flexes in the manner and to theextent described below.

[0028] Head

[0029] The toothbrush of this invention further comprises a resilientlyflexible head attached to the proximal end of the handle, the headincluding a pair of opposing faces, one of the pair being abristle-bearing face with bristles attached to and extending from theface, wherein at least one of the pair has one or moreelastomer-containing, transverse grooves therein.

[0030] Suitable materials for the head are the same as those for thehandle. Preferably the head and handle are co-moulded in a singleinjection moulding step, so that the head and handle form one continuouspiece. In any case the long axis of the handle defines a longitudinalaxis of the head. The head also has a transverse axis lying orthogonalto the longitudinal axis and generally parallel to the opposed faces.References to transverse or longitudinal herein refer to directionswhich are respectively parallel to these transverse and longitudinalaxes, unless indicated otherwise. The head itself is also generallyelongated, with its elongated axis also being a longitudinal axis.

[0031] The head includes transverse grooves on at least one of thebristle-bearing face and the opposing face, the grooves dividing thehead into segments. The grooves allow the head to flex or bend along itslongitudinal axis. This allows the brush head to flex so that itacquires a convex profile along the longitudinal axis when pressedagainst the teeth. This makes it particularly suitable for brushing thelingual or inside surfaces of the teeth. The grooves can be linear ornon-linear, such as curved or zigzag. Non-linear grooves help to offsetcompression stress in the elastomeric material filling the grooves asthe head bends. The term ‘transverse grooves’ as used herein can alsoencompass grooves whose main axis, as defined by the straight linejoining the start and endpoints of the grooves is offset from thetransverse axis of the head by an angle of up to and including 45°. Inpreferred embodiments both the bristle-bearing face and the opposingface include one or more transverse grooves therein.

[0032] The head also includes one or more longitudinal grooves on atleast one of the bristle-bearing face and the opposing face. The term‘longitudinal grooves’ as used herein can also encompass grooves whosemain axis, as defined by the straight line joining the start andendpoints of the grooves is offset from the ‘longitudinal axis of thehead by an angle of up to 45°. Longitudinal grooves can allow, forexample, the outer longitudinal rows of bristles to flex away from theinner ones. They also act as elastomer supply channel(s) to thetransverse grooves as described below.

[0033] Where there are grooves on both of the opposing faces, grooves onone face can be directly opposed to grooves on the other face orpartially or wholly offset. Preferably, the grooves are directly opposedor only partially offset.

[0034] The grooves, which separate the segments of the head, also definehinges, which are thinned regions of the head at the base of thegrooves.

[0035] The grooves can be of variable width and depth and the distancesbetween grooves can also be varied. In this manner the flexibility ofthe head along the length and/or across the breadth of the head can bemodified. Preferably only transverse grooves are varied in this way.Changing the depth of the grooves controls the location and thickness ofthe hinges which connect the segments. For a toothbrush head of betweenabout 4 to about 6 mm thickness, typically about 5 mm, suitable groovedepths are in the range from about 1.4 to about 3 mm, preferably fromabout 1.5 to about 2.8 mm. Suitable hinge thicknesses are in the rangefrom about 0.4 to about 2.0 mm, preferably from about 0.5 to about 1.5mm. Where transverse grooves are used then, desirably, the hinges whichare or will be nearer to the handle are less flexible than those whichare or will be more remote from it. In this way more uniform bending ofthe head can be achieved. The variation in flexibility can be achievedby varying the hinge thicknesses. In a preferred embodiment the hingenearest the handle is up to about 3 times, preferably up to about 2times as thick as the hinge most remote from the handle. An exemplaryset of hinge thicknesses for a toothbrush with 3 transverse grooves arerespectively about 1.2, 0.6 and 0.6 mm reading from the handle end. Ifidentical hinges are used along the brush head then there is a tendencyfor flexing of the head to occur predominantly at the hinge nearest thehandle. The depth of grooves on the bristle bearing face can bedifferent to those on the opposing face. Preferably the grooves on thebristle-bearing face are less deep than those on the opposing face. Inembodiments where there is elastomer in the grooves on both faces, thisallows more elastomer to be put under compression than under tension.The elastomer to segment bonds are stronger under compression than undertension.

[0036] Increasing the width of the grooves increase the gap between thesegments and therefore the length of the hinges, which increases theirflexibility. However, since it is preferred to insert bristles into thesegments rather than into the elastomer, increased groove length alsoleaves less space for the bristles, within a given head size. Suitablegroove widths are in the range from about 0.3 to about 3.0 mm,preferably from about 1.2 to about 2.0 mm. The grooves are preferablytapered slightly inwards towards the bottom of the groove, suitablyconverging at an angle of from about 3 to about 10°, to facilitatemoulding. As the brush is flexed the width of the groove changes, morerapidly at the top of the groove than at the bottom of the groove, therelative change being a function of the groove width and depth. Sincethis change in groove width results in compression or tension ofelastomer contained within the groove, it can be seen that, for a givenelastomer, the groove geometry can be used to control the flex angle.

[0037] The hinges can be the full length of the grooves or, preferably,there can be one or more gaps in or to the side of the hinges thegrooves in these regions being the full depth of the head. The gapallows elastomer to flow from one face to the other during the mouldingprocess so that elastomer can be used on both sides of the head and yetstill supplied from a single injection point. In a preferred embodiment,the hinges are discontinuous, with two or more hinges, preferably justtwo, connecting each segment to its neighbour or to the handle. In thisembodiment there are gaps between the hinges and to each side. In lineargrooves, the hinge widths are not generally critical, provided that theyare such that gaps are still created, however, wide hinges can besubject to distortion if they are used within a non-linear groove.Suitable hinge widths are in the range from about 0.5 to about 4.0 mm,preferably from about 1.0 to about 3.0 mm.

[0038] It is preferred that each hinge is located between the two facesand at a distance of at least about 10%, preferably at least about 20%,more preferably at least about 30% of the depth of the head from each ofthe faces. The distance of the hinge from the face is measured by theperpendicular line drawn from the top of the face to the nearestboundary surface of the centre of the hinge. Locating the hinges awayfrom the faces of the brush means that they are subject to lessstretching or compression as the head is flexed and improves theirdurability. In a particularly preferred embodiment, the brush head hastransverse grooves which are arranged in pairs such that one member ofeach pair is on each face and directly opposes the other member of thepair, with one or more hinges therebetween connecting the segments sothat each hinge is located between the two faces and at a distance of atleast about 10%, preferably at least about 20%, more preferably at leastabout 30% of the depth of the head from each of the faces.

[0039] The grooves on at least one face of the brush contain elastomer,preferably bonded to the segments of the head. The term ‘elastomer’herein refers to a material which is both elastically compressible andelastically extensible. Thus when the head is flexed in a directionorthogonal to the opposed faces, the elastomer is put either undertension or under compression. The elastomer has the effect of limitingthe head flexibility thereby reducing the stretching or compression ofthe hinges and of limiting the stress at the bond between the elastomerand the head segments. A more durable head is thus obtained. Preferably,grooves on both the bristle-bearing face and the opposing face containelastomer so that elastomer is put under compression whichever directionis chosen. The elastomer on the opposed face is of course put undertension but the tensile stress on the elastomer to segment bonds islimited and is shared with the hinge material.

[0040] Preferably all of the grooves are wholly filled with theelastomer. Complete filling of the grooves has an advantage of, forexample, avoiding contamination of the grooves by toothpaste deposits.The grooves can be partially filled though, provided that sufficientelastomer is used to give effective moderation of the flexibility of thehead.

[0041] The whole head has a conventional, generally flattened shape butremains flexible when compared to that of a conventional brush. By‘flexible’ is meant herein that when a 3 Newton force is applied to oneend of the head, the other end being held fixed, the end to which theforce is applied will deflect through an angle of at least 2°. The endof the head which is to be held fixed is defined by the line which isperpendicular to the axis along which bending takes place and whichtouches the first row of bristles. In the preferred embodiments havingtransverse grooves, where the head bends along the longitudinal axis,the end should be that which connects to the handle. The end of the headwhere the force is to be applied is the opposite end of the head at thefurthest point away along the bending axis. By ‘resiliently flexible’ ismeant that when the 3 Newton force is removed, the head will return toits original position without the application of external force. Theangle through which the head bends when a 3 Newton force is applied asabove is referred to herein as the flex angle. The flex angle canconveniently be measured by measuring the vertical displacement (y) ofthe free end of the head under a 3 Newton force and the distance y andthe distance between the clamping point and the application of the force(x), the flex angle being derived by the relationship tan(flexangle)=y/x. In preferred embodiments the flex angle is at least 3°, morepreferably at least 5° and it can be as high as 15° or more. Theconstruction of the head, in particular the dimensions of the groovesand hinges, the extent of elastomer filling of the grooves and hardnessof the elastomer is, however, such that the flex angle is limited toless than about 40°, preferably less than 30°, more preferably less than20°. This has been found to give an acceptable degree of flexibility forusers without exposing the hinges and elastomer-segment bonds to unduestress.

[0042] In highly preferred embodiments, only one of the opposed faces isbristle-bearing and when the head is in its normal unstressed state, thefree ends of bristles lying along a longitudinal axis of the brush forma generally concave profile. In highly preferred embodiments, thebristle-bearing face is concavely shaped. In these embodiments the headpreferably has a flex angle such that the bristle-bearing face of thehead is able to bend to the extent that the free ends of bristles lyingalong a longitudinal axis of the brush form a generally convex profile.The face of the head can be concave along either or both of theorthogonal axes of the head lying within the general plane of thebristle-bearing face. Where the face is concave along the longitudinalaxis, the radius of curvature may vary along the length of the head. Theradius of curvature is preferably from 10 to 500 mm, more preferablyfrom 15 to 250 mm, especially from 25 to 150 mm.

[0043] The brush head has bristles extending from one of the pair ofopposing faces. The bristles can be made of any of the materials wellknown in the art. Suitable bristle materials herein are polyester andnylon, such as Dupont Nylon 612. The bristles are preferably of circularcross-section but can also be of other cross-sections including, but notlimited to, rectangular, hexagonal and trilocular. Furthermore, thediameter and length of the bristles can vary within the usual dimensionsknown by a person skilled in the art. The bristles are generallyconventionally grouped into tufts and can be attached to the brush headby a variety of processes. Preferred processes herein are stapling andfusion. The bristles can be inserted into the segments or the elastomer,preferably into the harder material of the segments. Cutting andend-rounding of the bristles can be done using any of the methodscommonly known in the art.

[0044] Supply Channels

[0045] A further essential feature of the toothbrush of this inventionis one or more elastomer supply channels extending between theelastomeric handle regions and the transverse grooves, whereby at leastone, preferably all, of the elastomeric handle regions and thetransverse grooves can be filled with elastomer from a single injectionpoint. In the head these are conveniently provided by one or morelongitudinal grooves intersecting the transverse grooves.

[0046] In especially preferred embodiments the brush head comprises bothtransverse grooves on each of the opposed faces so that the head canbend along the longitudinal axis and at least one longitudinal groovewhich connects the transverse grooves and extending along the handle toconnect further with the voids that are used to form the handle grips.The longitudinal groove permits molten elastomer to flow from aninjection point to the elastomeric handle regions and then further tothe transverse grooves in the head.

[0047] This is generally achieved by a separate injection moulding stepafter the moulding of the handle and the segments of the head has beencompleted. Preferably, all of the elastomer is injected from a singleinjection point. A preferred method of making the toothbrush of theinvention comprises the step of injecting molten elastomer, preferablyat a temperature in the range from about 220° C. to about 260° C., morepreferably from about 230° C. to about 250° C., under pressure, into theinjection point and causing it to flow along the supply channel and intothe grooves. Suitable injection pressures are in the range from about 35MNm⁻² (350 bar) to about 50 MNm⁻² (500 bar), preferably from about 42MNm⁻² (420 bar) to about 48 MNm⁻² (480 bar).

[0048] In use, toothbrushes comprising the brush head of this inventioncan be used for cleaning the teeth by an entirely conventional toothbrushing hand action, preferably in a manner recommended by dentalhealth authorities. The brush head of the invention can also be used inelectrically driven toothbrushes or children's toothbrushes.

[0049] The invention will now be described by way of example only, withreference to the accompanying drawings in which:

[0050]FIG. 1 is a partial side view of a first embodiment of theinvention, depicting the toothbrush head with transverse grooves.Although the head is flat in its unstressed state, the bristles are cutto different lengths so that the bristle surface is concave along thelongitudinal direction.

[0051]FIG. 2 is a plan view of a toothbrush head showing transversegrooves, a longitudinal groove acting as a supply channel, anddiscontinuous hinges. The bristles are omitted for the sake of clarity.

[0052]FIG. 3 is a perspective view of a toothbrush according to theinvention. The bristles are omitted for the sake of clarity.

[0053]FIG. 4 is a perspective view of the toothbrush shown in FIG. 3with the elastomer not shown in order to show the hinges, grooves andsupply channel more clearly.

[0054]FIG. 5 is a schematic showing the measurement of the flex angle.

[0055] Referring to FIG. 1, the brush head (1) has substantiallyparallel top and bottom faces, comprising segments (2) flexiblyconnected by hinges of head material (3). The top and bottom faces carryequal numbers of generally parallel transverse grooves (4) filled withelastomer (5). A longitudinal groove (not shown) connects the transversegrooves and extends into the handle (8), acting as a supply channel.Tufts of bristles (6), extending from the top face, form a concavesurface (7) at their free ends. Referring to FIG. 2, a toothbrush head(1) is formed integrally at one end of a handle (8). The head includesthree pairs of transverse grooves (4), one of each pair being on each ofthe top and bottom surfaces. The transverse grooves are in the form ofwaves and a single longitudinal groove (9) connects the transversegrooves and extends into the handle, acting as a supply channel. Thegrooves are entirely filled with elastomer (5). The transverse groovesdefine segments of the head (2) which are connected to each other byhinges (3). There are gaps (10) between and to each side of the hingesso that in the gaps, the elastomer extends from top to bottom surfaces.

[0056] In FIGS. 3 and 4 the head (1) is co-moulded with the handle (8)and is concave along its longitudinal axis on the bristle-bearing(upper) surface. Voids (11) in the handle are filled with elastomer toprovide hand grips (16). The voids are connected to each other by alongitudinal groove (12) on the reverse side of the handle which extendsinto the head and connects the transverse grooves (4) as shown in theview in FIG. 2. The elastomer in the voids and the grooves is injectedfrom a single injection point (13) and is of a different colour to thehead material to give a distinctive appearance. The head has holes (14)disposed on the top surface thereof to accommodate tufts of bristles.

[0057]FIG. 5 illustrates the measurement of the flex angle. The head (1)is clamped (15) against the first row of bristles (6) at the end whichis attached to the handle (8) and a 3 Newton force (F) is applied to theopposite end. The dashed lines show the original position of the brushhead before the force is applied. The vertical displacement (y) of thefree end of the head under the force F is measured and the flex angle isderived from the distance y and the distance between the clamping pointand the application of the force (x) by the relationship tan(flexangle)=y/x.

What is claimed is:
 1. A toothbrush, comprising: i) an elongated handlehaving distal and proximal ends and one or more elastomeric handleregions therein; and ii) a resiliently flexible head attached to theproximal end of the handle, the head including a pair of opposing faces,one of the pair being a bristle-bearing face with bristles attached toand extending from the face, wherein at least one of the pair has one ormore elastomer-containing, transverse grooves therein; and iii) one ormore elastomer supply channels extending between the elastomeric handleregions and the transverse grooves, whereby at least one of theelastomeric handle regions and the transverse grooves can be filled withelastomer from a single injection point.
 2. A toothbrush according toclaim 1 wherein all of the elastomeric handle regions and the transversegrooves can be filled with elastomer from a single injection point.
 3. Atoothbrush according to claim 2 wherein at least one supply channelextends to the distal end of the handle.
 4. A toothbrush according toclaim 3 wherein the elastomer injection point is located at the distalend of the handle.
 5. A toothbrush according to claim 4 wherein both thebristle-bearing face and the opposing face include transverse groovestherein.
 6. A toothbrush according to claim 5 wherein the transversegrooves divide the head into segments which are flexibly connected byhinges, wherein each hinge is located between the opposing faces and ata distance of at least about 10% of the depth of the head from each ofthe faces, the hinges being less than the full width of the head.
 7. Atoothbrush according to claim 6 wherein handle is made from an opaquematerial and the supply channel passes from one face of the handle toits opposite face so that, when filled with elastomer, the supplychannel appears to be discontinuous.
 8. A method for making thetoothbrush of any of the preceding claims comprising the step ofinjecting molten elastomer, under pressure, into the injection point andcausing it to flow along the supply channel and into the grooves.